We Keep Coding

Which pattern or method to use when calling a regex check method in multiple if statements?

I created a factory pattern in my class.
In this class I injected classes which implements Command interface based on incoming String parameter.
Factory class
#Component
#RequiredArgsConstructor
public class CommandFactory {
private final ACommand aCommand;
private final BCommand bCommand;
private final CCommand cCommand;
private final DCommand dCommand;
private final ECommand eCommand;
private final FCommand fCommand;
public Command createCommand(String content) {
if (aCommand.isMatching(content)) {
return aCommand;
} else if (bCommand.isMatching(content)) {
return bCommand;
} else if (cCommand.isMatching(content)) {
return cCommand;
} else if (dCommand.isMatching(content)) {
return dCommand;
} else if (eCommand.isMatching(content)) {
return eCommand;
} else if (fCommand.isMatching(content)) {
return fCommand;
} else {
return null;
}
}
In isMatching() method there are different regex'es and I try to figure out how this incoming String should be processed.
I am looking for a cleaner way to get rid of these sequential if statements. Because whenever I create a new class into this factory I add another if statement.

Maybe Stream can help?
Stream<Command> stream = Stream.of(aCommand, bCommand, cCommand ...);
return stream.filter(x -> x.isMatching(content)).findFirst().orElse(null);
Now every time you add a new class, you just add a new object to the first line.

If you want to get rid of the sequential if statements you can use streams (like user Sweeper suggested) or loops and I would also suggest to return and optional which makes null handling clearer for the client.
Here are two suggested options to get rid of if else repetitions one with loops another with streams:
import java.util.Arrays;
import java.util.List;
import java.util.Optional;
public class CommandPatternExample {
private List<Command> candidates = Arrays.asList(new ACommand(), new BCommand(), new CCommand());
public Optional<Command> createCommand(String content) {
for(Command command : candidates) {
if(command.isMatching(content)) {
return Optional.of(command);
}
}
return Optional.empty();
}
public Optional<Command> createCommandStream(String content) {
return candidates.stream().filter(c -> c.isMatching(content)).findFirst();
}
}
interface Command<T> {
void execute(T obj);
boolean isMatching(String s);
}
class ACommand implements Command<String> {
#Override
public void execute(String obj) {
}
#Override
public boolean isMatching(String s) {
return "A".equals(s);
}
}
class BCommand implements Command<String> {
#Override
public void execute(String obj) {
}
#Override
public boolean isMatching(String s) {
return "B".equals(s);
}
}
class CCommand implements Command<String> {
#Override
public void execute(String obj) {
}
#Override
public boolean isMatching(String s) {
return "C".equals(s);
}
}

Map might be a good idea. Meaning if you place your command instances into a map as values where your key would be something that you could match against incoming String. Then instead of sequential search with Efficiency O(n) you can get much better performance O(1). This is a short answer.
Besides that There is an open source java library MgntUtils (wriiten by me) that contains some utility called "Self-instantiating factories" Basically it manages and the Factory for you. All you will need to do is to create a class that implements a certain interface and the utility will add it for you into a map based factory. It might be useful to you. Here is the link to an article that explains about the utilities in the library as well as where to get the library (Github and Maven central). In the article look for the paragraph "Lifecycle management (Self-instantiating factories)". Also library comes with a detailed written javadoc and code example for that feature.

How to do refactoring to eliminate type-code if it is used in validation rules?

Let's say we have to check some set of rules before adding a new element in a collection. Elements are objects of a few similar types. All type specific features are encapsulated in subclasses of an abstract class. Collection contains objects of this abstract class. The rules apply conditions for types along with other constraints. For that reason the abstract superclass of items has additional type code. New element can be added to collection but due to additional rules other elements in collection can be removed or replaced.
In the code that needs to be refactored, validation of the rules is implemented as one long block of code with nested control flow statements. Validation of the type code breaks encapsulation. Separate branches of the control flow statements cannot be defined as method of corresponding subclasses of collection elements because them need to check type and make changes to collection.
additional facts regarding type code in my case:
type code does not affect the behaviour of class
type code is immutable
type code is used by ItemsManager to resolve some rules before to add
new element to collection.
How to eliminate type code and separate rules from types?
Here is example of such problem:
Type specific features of Items are encpsulated in AbstractItem subclasses.add method of ItemManager class breaks encapsulation.Rule: item of Type2 must be removed if new item of Type1 with the same value of SomeUsefull property is adding to collection.
For simplicity implementation of ICloneable and IComparable interfaces is omitted. In real world items in collection are immutable and cloneable and the system of rules is quite tangled.
abstract class AbstractItem {
private int Type; // this would like to eliminate
private int SomeUseful;
protected AbstractItem(int Type, int Value) {
this.Type = Type;
this.SomeUseful = Value;
}
public int getType() { return this.Type; }
public int getSomeUseful() { return this.SomeUseful; }
#Override
public String toString() {
return String.format("Item{Type=%d, Value=%d}", Type, SomeUseful);
}
}
class ItemType1 extends AbstractItem {
ItemType1(int Value) { super(1, Value); }
}
class ItemType2 extends AbstractItem {
ItemType2(int Value) { super(2, Value); }
}
class ItemManager {
private java.util.ArrayList<AbstractItem> ListOfItems;
public ItemManager(){
this.ListOfItems = new java.util.ArrayList<AbstractItem>();
}
public void add(final AbstractItem newItem) {
// this code breaks encapsulation
switch (newItem.getType()) {
case 1:
// do some type dependent operations
for(AbstractItem i: this.ListOfItems) {
if (i.getType()==2 && i.getSomeUseful()==newItem.getSomeUseful()) {
this.ListOfItems.remove(i);
break;
}
}
break;
case 2:
// do some other type dependent operations
break;
default:
// throw error
}
this.ListOfItems.add(newItem);
}
#Override
public String toString() {
String str = String.format("ItemsManager content");
for(AbstractItem i: this.ListOfItems) {
str += String.format("\n\tType = %d, Value = %d", i.getType(), i.getSomeUseful());
}
return str;
}
}
public class Example1 {
public static void main(String[] arg) {
System.out.println("Example 1");
ItemManager im = new ItemManager();
im.add(new ItemType1(1));
im.add(new ItemType2(2));
im.add(new ItemType2(3));
im.add(new ItemType1(3));
System.out.println(im.toString());
}
}
/*
Example 1
ItemsManager content
Type = 1, Value = 1
Type = 2, Value = 2
Type = 1, Value = 3
*/

Starting from #dbugger's answer you can push it further.
You can use Double Dispatch to hide the type code. Still not a perfect solution because the parent knows too much about its children, but the type code is gone now.
It is hard to tell what a better solution might be with the example code you have given, because when you simplified, you removed all the information about the items involved. There might be something there that could be used for discrimination in some other way, allowing you to get rid of the double dispatch with shoudBeRemovedBecauseType1.
Here is the altered onAdd method from type 1
#Override
public List<AbstractItem> onAdd(List<AbstractItem> list) {
for (AbstractItem item : list) {
if (item.shoudBeRemovedBecauseType1(this)) {
list.remove(item);
break;
}
}
return list;
}
A new method in the base class
public boolean shoudBeRemovedBecauseType1(ItemType1 itemType1)
{
return false;
}
overridden in the type 2 subclass
#Override
public boolean shoudBeRemovedBecauseType1(ItemType1 itemType1)
{
return getSomeUseful() == itemType1.getSomeUseful();
}

It's not ideal, but it's a step towards getting some encapsulation and killing the switch statement...
add an onAdd method to the base class that takes the list as a parameter.
public java.util.ArrayList<AbstractItem> onAdd(java.util.ArrayList<AbstractItem> list) { return list; }
then override it in the sub classes, for example...
#Override
public java.util.ArrayList<AbstractItem> onAdd(java.util.ArrayList<AbstractItem> list) {
for(AbstractItem i: this.ListOfItems) {
if (i.getType()==2 && i.getSomeUseful()==this.getSomeUseful()) {
list.remove(i);
break;
}
}
return list;
}
then rewrite the ItemManager add method to just call the sub classes' onAdd methods...
public void add(final AbstractItem newItem) {
this.ListOfItems = newItem.onAdd(this.ListOfItems);
this.ListOfItems.add(newItem);
}

Replacing if else statement with pattern

I have a if else statement which might grow in the near future.
public void decide(String someCondition){
if(someCondition.equals("conditionOne")){
//
someMethod("someParameter");
}else if(someCondition.equals("conditionTwo")){
//
someMethod("anotherParameter");
}
.
.
else{
someMethod("elseParameter");
}
}
Since, this is already looking messy, I think it would be better if I can apply any design patterns here. I looked into Strategy pattern but I am not sure if that will reduce if else condition here. Any suggestions?

This is a classic Replace Condition dispatcher with Command in the Refactoring to Patterns book.
Basically you make a Command object for each of the blocks of code in your old if/else group and then make a Map of those commands where the keys are your condition Strings
interface Handler{
void handle( myObject o);
}
Map<String, Handler> commandMap = new HashMap<>();
//feel free to factor these out to their own class or
//if using Java 8 use the new Lambda syntax
commandMap.put("conditionOne", new Handler(){
void handle(MyObject o){
//get desired parameters from MyObject and do stuff
}
});
...
Then instead of your if/else code it is instead:
commandMap.get(someCondition).handle(this);
Now if you need to later add new commands, you just add to the hash.
If you want to handle a default case, you can use the Null Object pattern to handle the case where a condition isn't in the Map.
Handler defaultHandler = ...
if(commandMap.containsKey(someCondition)){
commandMap.get(someCondition).handle(this);
}else{
defaultHandler.handle(this);
}

Let's assume that we have such code (which is the same as yours):
public void decide(String someCondition) {
if(someCondition.equals("conditionOne")) {
someMethod("someParameter");
}
else if(someCondition.equals("conditionTwo")) {
someMethod("anotherParameter");
}
else {
someMethod("elseParameter");
}
}
Assuming that you don't want to refactor other parts of the application and you don't want to change method signature there are possible ways in which it could be refactored:
Warning - You should use generic versions of mentioned patterns.
I showed non generic ones because it is easier to read them.
Strategy + Factory Method
We can use Strategy and Factory Method patterns. We also take advantage of polymorphism.
private final StrategyConditionFactory strategyConditionFactory = new StrategyConditionFactory();
public void decide(String someCondition) {
Strategy strategy = strategyConditionFactory.getStrategy(someCondition)
.orElseThrow(() -> new IllegalArgumentException("Wrong condition"));
strategy.apply();
}
It would be better to design it in a way that else condition is included in the factory, and developer calls it on purpose. In such case we throw exception when condition is not meet. Alternatively we could write it exactly as it was in question. If you want so instead of .orElseThrow(() -> new IllegalArgumentException("Wrong condition")); put .orElse(new ElseStrategy());
StrategyConditionFactory (factory method):
public class StrategyConditionFactory {
private Map<String, Strategy> conditions = new HashMap<>();
public StrategyConditionFactory() {
conditions.put("conditionOne", new ConditionOneStrategy());
conditions.put("conditionTwo", new ConditionTwoStrategy());
//It is better to call else condition on purpose than to have it in the conditional method
conditions.put("conditionElse", new ElseStrategy());
//...
}
public Optional<Strategy> getStrategy(String condition) {
return Optional.ofNullable(conditions.get(condition));
}
}
Strategy interface:
public interface Strategy {
void apply();
}
Implementations:
public class ConditionOneStrategy implements Strategy {
#Override
public void apply() {
//someMethod("someParameter");
}
}
public class ConditionTwoStrategy implements Strategy {
#Override
public void apply() {
//someMethod("anotherParameter")
}
}
public class ElseStrategy implements Strategy {
#Override
public void apply() {
//someMethod("elseParameter")
}
}
Usage (simplified):
public void strategyFactoryApp() {
//...
decide("conditionOne");
decide("conditionTwo");
decide("conditionElse");
//...
}
Strategy + Factory Method - this particular case (where only parameter changes)
We can use the fact that in this case we always call the same method, only parameter changes
We change our base strategy interface to abstract class with getParameter() method and we make new implementations of this abstract class. Other code remains the same.
public abstract class Strategy {
public abstract String getParameter();
public void apply() {
someMethod(getParameter());
}
private void someMethod(String parameter) {
//someAction
}
}
Implementations:
public class CondtionOneStrategy extends Strategy {
#Override
public String getParameter() {
return "someParameter";
}
}
public class CondtionTwoStrategy extends Strategy {
#Override
public String getParameter() {
return "anotherParameter";
}
}
public class ElseStrategy extends Strategy {
#Override
public String getParameter() {
return "elseParameter";
}
}
Enum + enum kinda "factory"
We might use Enum to implement strategy and instead of factory method we can use valueOf() from enum.
public void decide(String someCondition) {
ConditionEnum conditionEnum = ConditionEnum.valueOf(someCondition);
conditionEnum.apply();
}
Condition enum:
public enum ConditionEnum {
CONDITION_ONE {
#Override
public void apply() {
//someMethod("someParameter");
}
},
CONDITION_TWO {
#Override
public void apply() {
//someMethod("anotherParameter");
}
},
CONDITION_ELSE {
#Override
public void apply() {
//someMethod("elseParameter");
}
};
//...more conditions
public abstract void apply();
}
Usage (simplified):
public void enumFactoryApp() {
//...
decide("CONDITION_ONE");
decide("CONDITION_TWO");
decide("CONDITION_ELSE");
//...
}
Notice that you will get IllegalArgumentException when enum type has no constant with the specified name.
Command + Factory
The difference between strategy and command is that command holds also state, so if you have for example compute(int a, int b, String someCondition) and you want to refactor it with strategy including it's signature change you can reduce it to compute(int a, int b, ComputeStrategy computeStrategy) with command you can reduce it to one argument compute(ComputeCommand computeCommand). In this case we also take advantage of polymorphism similarly to strategy pattern case.
CommandConditionFactory commandConditionFactory = new CommandConditionFactory();
public void decide(String someCondition) {
Command command = commandConditionFactory.getCommand(someCondition)
.orElseThrow(() -> new IllegalArgumentException("Wrong condition"));
command.apply();
}
It would be better to design it in a way that else condition is included in the factory, and developer calls it on purpose. In such case we throw exception when condition is not meet. Alternatively we could write it exactly as it was in question. If you want so instead of .orElseThrow(() -> new IllegalArgumentException("Wrong condition")); put .orElse(new ElseCommand());
CommandConditionFactory (factory method):
public class CommandConditionFactory {
private Map<String, Command> conditions = new HashMap<>();
public CommandConditionFactory() {
conditions.put("conditionOne", new ConditionOneCommand("someParameter"));
conditions.put("conditionTwo", new ConditionTwoCommand("anotherParameter"));
//It is better to call else condition on purpose than to have it in the conditional method
conditions.put("conditionElse", new ElseCommand("elseParameter"));
//...
}
public Optional<Command> getCommand(String condition) {
return Optional.ofNullable(conditions.get(condition));
}
}
Command interface:
public interface Command {
void apply();
}
Implementations (there is some redundancy, but It is there to show how command should look in more general case where instead of someMethod() we have three different methods):
public class ConditionOneCommand implements Command {
private final String parameter;
public ConditionOneCommand(String parameter) {
this.parameter = parameter;
}
#Override
public void apply() {
//someMethod(parameter);
}
}
public class ConditionTwoCommand implements Command {
private final String parameter;
public ConditionTwoCommand(String parameter) {
this.parameter = parameter;
}
#Override
public void apply() {
//someMethod(parameter);
}
}
public class ElseCommand implements Command {
private final String parameter;
public ElseCommand(String parameter) {
this.parameter = parameter;
}
#Override
public void apply() {
//someMethod(parameter);
}
}
Usage (simplified):
public void commandFactoryApp() {
//...
decide("conditionOne");
decide("conditionTwo");
decide("conditionElse");
//...
}
Command + Factory - This particular case.
This in fact isn't a real command pattern just a derivative. It takes advantage of the fact that in this case we are always calling the same method someMethod(parameter) and only the parameter changes.
Abstract class:
public abstract class Command {
abstract void apply();
protected void someMethod(String parameter) {
//someAction
}
}
Implementation (the same for all 3 conditional cases):
public class CommandImpl extends Command {
private final String parameter;
public CommandImpl (String parameter) {
this.parameter = parameter;
}
#Override
public void apply(){
someMethod(parameter);
}
}
Factory, please notice that there is only one command implementation, only parameter changes:
public class CommandConditionFactory {
Map<String, Command> conditions = new HashMap<>();
public CommandConditionFactory() {
conditions.put("conditionOne", new CommandImpl("someParameter"));
conditions.put("conditionTwo", new CommandImpl("anotherParameter"));
//It is better to call else condition on purpose than to have it in the conditional method
conditions.put("conditionElse", new CommandImpl("elseParameter"));
//...
}
public Optional<Command> getCommand(String condition) {
return Optional.ofNullable(conditions.get(condition));
}
}
Nested if's
Note that even if you have nested ifs sometimes it is possible to refactor them and use one of the mentioned techniques.
Lets say that we have following code:
public void decide2(String someCondition, String nestedCondition) {
if(someCondition.equals("conditionOne")) {
if(nestedCondition.equals("nestedConditionOne")){
someLogic1();
}
else if(nestedCondition.equals("nestedConditionTwo")){
someLogic2();
}
}
else if(someCondition.equals("conditionTwo")) {
if(nestedCondition.equals("nestedConditionThree")){
someLogic3();
}
else if(nestedCondition.equals("nestedConditionFour")){
someLogic4();
}
}
}
You could refactor it using mathematical logic rules:
public void decide2(String someCondition, String nestedCondition) {
if(someCondition.equals("conditionOne")
&& nestedCondition.equals("nestedConditionOne")) {
someLogic1();
}
else if(someCondition.equals("conditionOne")
&& nestedCondition.equals("nestedConditionTwo")) {
someLogic2();
}
else if(someCondition.equals("conditionTwo")
&& nestedCondition.equals("nestedConditionThree")) {
someLogic3();
}
else if(someCondition.equals("conditionTwo")
&& nestedCondition.equals("nestedConditionFour")) {
someLogic4();
}
}
and then you can use strategy, enum or command. You just have a pair of Strings <String, String> instead of single String.
Decision Tables
When you have nested ifs that couldn't be refactored as mentioned you can implement your own decision tables or use some ready to go decision tables solution. I won't give the implementation there.
Rules Engine
When you have nested ifs that couldn't be refactored as mentioned you can also implement your own simple rules engine. You should use it only if you have many nested ifs, otherwise it is triumph of form over content.
For very complicated Business Logic there are professional Rule Engines like Drools.
I won't give the implementation there.
One more thing
In the example that you gave there is a high possibility that someone introduced these ifs, but they are totally redundant. And we can check it by trying to refactor decide method signature to make it take some other argument and to refactor surrounding code that is calling our method. By doing so we are getting rid of our Factory Method. There are examples that present how the code might look when it occurs that these ifs were redundant.
Strategy
Decide method:
public void decide(Strategy strategy) {
strategy.apply();
}
Usage (simplified):
public void strategyApp() {
//...
decide(new ConditionOneStrategy());
decide(new ConditionTwoStrategy());
decide(new ElseStrategy());
//...
}
Enum
Decide method:
public void decide(ConditionEnum conditionEnum) {
conditionEnum.apply();
}
Usage (simplified):
public void enumApp() {
//...
decide(ConditionEnum.CONDITION_ONE);
decide(ConditionEnum.CONDITION_TWO);
decide(ConditionEnum.CONDITION_ELSE);
//...
}
Command
Decide method:
public void decide(Command command) {
command.apply();
}
Usage (simplified):
public void commandApp() {
//...
decide(new ConditionOneCommand("someParameter"));
decide(new ConditionTwoCommand("anotherParameter"));
decide(new ElseCommand("elseParameter"));
//...
}
In fact it is quite specific case, there are cases in which for example we have to use simple type like String, because it comes from the external system or condition is based on integer from input so we can't refactor the code so easily.

The general recommendation by Martin Fowler is to
Replace Conditional with Polymorphism.
In terms of design patterns this would often be the Strategy Pattern
Replace Conditional Logic with Strategy.
If you have a small, finite set of conditions, I recommend to use an enum to implement the Strategy Pattern (provide an abstract method in the enum and override it for each constant).
public enum SomeCondition{
CONDITION_ONE{
public void someMethod(MyClass myClass){
//...
}
},
CONDITION_TWO{
public void someMethod(MyClass myClass){
}
}
public abstract void someMethod(MyClass myClass);
}
public class MyClass{
//...
public void decide(SomeCondition someCondition){
someCondition.someMethod(this);
}
}
If it's really just a parameter you want to pick, then you could define the enum like this instead:
public enum SomeCondition{
CONDITION_ONE("parameterOne"),
CONDITION_TWO("parameterTwo");
private final String parameter;
private SomeCondition(String parameter){
this.parameter = parameter;
}
public String getParameter(){
return parameter;
}
}
public class MyClass{
//...
public void decide(SomeCondition someCondition){
someMethod(someCondition.getParameter());
}
}

Another way to solve the current problem is to use Factory Pattern. This provides functionality to extract a factory method that returns an object of a given type and performs the operation based on the concrete object behavior.
public interface Operation {
String process(String a, String b);
}
The method takes two string as input and returns the result.
public class Concatenation implements Operation {
#Override
public String process(String a, String b) {
return a.concat(b);
}
}
public class Join implements Operation {
#Override
public String process(String a, String b) {
return String.join(", ", a, b);
}
}
And then we should define a factory class which returns instances of Operation based on the given operator:
public class OperatorFactory {
static Map<String, Operation> operationMap = new HashMap<>();
static {
operationMap.put("concatenation", new Concatenation());
operationMap.put("join", new Join());
// more operators
}
public static Optional<Operation> getOperation(String operator) {
return Optional.ofNullable(operationMap.get(operator));
}
}
And now we can use it:
public class SomeServiceClass {
public String processUsingFactory(String a, String b, String operationName) {
Operation operation = OperatorFactory
.getOperation(operationName)
.orElseThrow(() -> new IllegalArgumentException("Invalid Operation"));
return operation.process(a, b);
}
}

I guess you must have already considered it, but if you are using JDK 7 or above, you can switch on strings. That way your code can look cleaner than a bunch of if-else statements.

How to have a method have different input types java

I have a program on my computer that simulates a server on the internet and the fake server needs to be able to send multiple data types to some classes. Like for instance at one point of the program the server needs to send an int to a class then convert that int to a string and send it to another.
Basically what I am asking is if a method can have multiple data types for an input(Does this make sense? if not ill try to explain better). Is there any way to do this without creating many different methods?
Edit: Also is there a way to tell the difference between the types passed in (to prevent errors)

You can have a method which takes Object which is any type. In Java 5.0 and later primitives will be auto-boxed and passed as an object as well.
void method(Object o);
can be called using
method(1);
method("hello world");
method(new MyClass());
method(null);

If I understand correctly, you're asking if a method foo() can have multiple different inputs for its parameters
That way foo(Integer i) and foo(String s) are encased in the same method.
The answer: yes, but it's not pretty
foo(Object o)
Is your method declaration
Now you need to sort out the different types of possibilities
if(o instanceof Integer){
stuff();
} else if (o instanceof String){
moreStuff();
}
Just chain those else/if statements for the desired result.

What you want are Generic methods or classes.
to check what type an object is you'll have to use the 'instanceof' method
you can either make an entire class generic or just a single method, an example of a generic class:
package javahowto;
public class Member<T> {
private T id;
public Member(T id) {
this.id = id;
}
public T getId() {
return id;
}
public void setId(T id) {
this.id = id;
}
public static void main(String[] args) {
Member<String> mString = new Member<String>("id1");
mString.setId("id2");
System.out.printf("id after setting id: %s%n", mString.getId());
//output: id after setting id: id2
Member<Integer> mInteger = new Member<Integer>(1);
mInteger.setId(2);
System.out.printf("id after setting id: %d%n", mInteger.getId());
//output: id after setting id: 2
}
Now you now what to look for I'm sure you'll find the best solution to your problem.
check out:
http://download.oracle.com/javase/tutorial/java/generics/index.html
http://en.wikipedia.org/wiki/Generics_in_Java
...

Well I have also wondered and wrote below block. I think instanceof better but I tried getclass.
public static void main(String[] args){
System.out.println(method("This is a test"));
}
private static String method(Object o){
System.out.println(o.toString());
String status = "";
String className;
String[] oList = {"Double","Integer","String","Double","Float","Byte","Short","Long","Character","Boolean" };
for(int i = 0;i<oList.length;i++){
className = "java.lang." + oList[i];
Class testClass;
try {
testClass = Class.forName(className);
if(o.getClass().equals(testClass)){
status = "Your object is " + oList[i];
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
return status;
}

You could use the "hashed adapter" pattern.
Public interface Adapter {
Public void handle(object o);
}
Public class StringAdapter implements Adapter {
Public void handle(String st) { // stuff ...
}
Public class IntegerAdapter implements Adapter {
Public void handle(Integer intgr) { // stuff ...
}
Private static final Map adapters = new HashMap();
Adapters.put(string.class, new stringAdapter());
Adapters.put(Integer.class, new IntegerAdapter());
Public void handleMe(Object o) {
Adapters.get(o.getClass()).handle(o);
}
Ive always liked this more than the ol' cascade of ifs and else's.
On my iPad so sorry about formatting and terseness and speellling.

remove duplication

I have a class contains 10 methods which are doing almost the same things apart from one key event. Two examples are given below:
Public String ATypeOperation(String pin, String amount){
doSomething();
doMoreStuff();
requestBuilder.buildATypeRequest(pin, amount);
doAfterStuff();
}
Public String BTypeOperation(String name, String sex, String age){
doSomething();
doMoreStuff();
requestBuilder.buildBTypeRequest(name, sex, age);
doAfterStuff();
}
As you can see from the above methods, they are similar apart from calling different methods provided by requestBuilder. The rest 8 are similar too. There is a lot duplicated code here. I feel there is a better way to implement this, but don’t know how. Any ideas and suggestions are appreciated.
Thanks,
Sarah

Use something like RequestBuilder, that accepts all these kinds of parameters:
public RequestBuilder {
// setters and getters for all properties
public Request build() {
doStuff();
Request request = new Request(this);
doAfterStuff();
return request;
}
}
and then
new RequestBuilder().setAge(age).setName(name).build();

What’s the nearest substitute for a function pointer in Java?
Function Pointers in Java

interface RequestBuilder {
void doStuff(params);
}
public RequestBuilder getARequestBuilder() {
return new RequestBuilder() {
void doStuff(params) {
// impl.details
}
}
}
public RequestBuilder getBRequestBuilder() {
return new RequestBuilder() {
void doStuff(params) {
// impl.details
}
}
}
public String buildRequest(yourParams, RequestBuilder builder){
doBefore();
builder.doStuff(yourParams);
doAfter();
}
I think this is called the Strategy pattern. It looks a lot like the Command pattern but because you encapsulate an algorithm it seems to be Strategy :)
What Bozho suggest is the Builder pattern.
I recommend you browse through a list of patterns some time, or buy Head First Patterns. Really fun reading.

You could pass the builder object to a generic buildRequest method. Since not only the algorithm but also the arguments vary, i put them into the builder. I dont think thats a nice solution but i wanted to show a command pattern here :D (Extraneon showed how to decouple params and command)
// call somewhere in the code:
Builder b = new BTypeBuilder();
b.age = "20"; b.sex = "female"; b.name = "eve";
String res = buildRequest(b);
Public String buildRequest(Builder builder)
{
doSomething();
doMoreStuff();
builder.build();
doAfterStuff();
}
// Command pattern
class BTypeBuilder implements Builder
{
String name, age, sex;
// Constructor here
void build()
{
// Do your stuff here
}
}
class ATypeBuilder implements Builder
{
String pin, amount;
// Constructor here
void build()
{
// Do your stuff here
}
}
public interface Builder
{
void build();
}

In addition to other answers, this might also be useful for you (If you want to just plugin your method, not using your parameters for 'before' and 'after' methods)
interface Function0<R> {
R apply();
}
public void performOperation(Function0<Void> operation) {
doSomething();
doBeforeStuff();
operation.apply();
doAfterStuff();
}
then you could use it like this,
final RequestBuilder builder = new RequestBuilder();
performOperation(new Function0<Void>() {
public Void apply() {
builder.buildATypeRequest("1234", "2445");
return null;
}
});
performOperation(new Function0<Void>() {
public Void apply() {
builder.buildBTypeRequest("1234", "2445", "1234");
return null;
}
});

Instead of sending a long parameter list just push all the parameters in a map and send that map as argument.